The Mackinac Bridge in Michigan spans five miles and is one of the longest suspension bridges in the world with the roadway soaring more than 200 feet over Lake Michigan. The bridge's dimensions provide stunning views of the surrounding landscape, but those vistas can be stomach-churning for people with gephyrophobia, or an abnormal fear of crossing bridges.

Between 1,200 to 1,400 calls are made every year to the bridge's Drivers Assistance Program that provides motorists with a crew member to drive them across if they're too afraid to drive themselves.

After the Thursday collapse of a highway bridge in Mount Vernon, Wash., the number of calls might increase with more fearful drivers wanting to be chauffeured across the Mackinac Bridge. But experts say phobias like gephyrophobia are sometimes more complicated in their origins.

Dr. Frank Schneier, a professor of clinical psychiatry at Columbia University and research psychiatrist at the New York State Psychiatric Institute, said many people who're afraid to cross bridges are also suffering from agoraphobia, an anxiety disorder triggered by a fear of feeling trapped.

"They have intense anxiety symptoms or panic attacks," Schneier said. "It's not so much the idea that bridges are [going to collapse]. It's that they are places you can't escape from."

About 0.8 percent of Americans older than 18 have a form of agoraphobia, according to the National Institute of Health.

"There are techniques that can help people overcome these kinds of fears," Schneier said, citing therapy and anti-anxiety mediation as options for drivers to ease their worries.

But for those who haven't conquered their fear of crossing the Mackinac Bridge, the Driver's Assistance Program is another option. Bob Sweeney, the secretary of the Mackinac Bridge, said phone booths on either side of the bridge allow motorists the chance to call the program. Some even use it during their commute to and from work.

"There's a truck driver, who comes once month," Sweeney said. "He gets into a sleeper behind the cab and lays down for the whole trip [under a blanket]. It's amazing."

Only one crew member is available during the night shift, so a toll operator has to pitch in and drive a second car that picks up the crew member for the return trip to the opposite side of the bridge.

The Mackinac Bridge isn't the only bridge that provides the extra service for fearful drivers. A similar program exists for New York City's Tappan Zee Bridge. The New York Thruway Authority allows motorists afraid of driving across the bridge to make an appointment to be chauffeured over.

But a New York Thruway Authority representative estimated that the service is used far less than the Michigan program, likely only a handful of times annually.

Schneier said such programs to ferry scared drivers across bridges can be helpful to keep traffic moving but don't solve the core of the problem and that people should seek help if their fears become incapacitating.

"It's a patch to get the person over the bridge that day," Schneier said. "Most people, with the right kind of help, can overcome these disorders if they become debilitating."

For some people, however, even being chauffeured over the bridge is too much. Sweeney said his own brother-in-law is too afraid to drive across the Mackinac Bridge and, as a result, has never been to his home in Michigan's Upper Peninsula, which is joined to the state's Lower Peninsula by the bridge.

"Surprisingly, there's a lot of people who [have this] phobia," Sweeney said. "I just found out my brother-in-law is so afraid they stay [on the other side of the bridge.]"

For an upcoming family visit, Sweeney's brother-in-law is planning to take two ferries to make the trip.